1. Field of the Invention (Technical Field)
The present invention relates to valves for controlling the flow of fluids, particularly gases, and more specifically to valves for more safely regulating the flow of oxygen gas.
2. Background Art
Oxygen is widely used in many medical and industrial applications. When a portable source of oxygen is required, it is almost universally supplied in the form of molecular oxygen (O2) under pressure in a cylindrical steel or aluminum container. Oxygen commonly also is transported in such cylinders. The cylinders are equipped with a valve, used to open and close the cylinder for emptying and refilling. A pressure regulator often also is attached to the cylinder valve.
Oxygen cylinder valves, as they exist today, have been implicated in numerous fire incidents with sometimes catastrophic results. When a cylinder valve seat ignites, the attached regulator or manifold system is subjected to strong kindling chain mechanisms that will often lead to fires downstream of the cylinder valve.
The xe2x80x9cplug typexe2x80x9d cylinder valves presently in common use comprise a rotating threaded seat plug that translates due to the rotation of a hand wheel mounted on the top of the valve itself. The plug incorporates a relatively large nonmetallic seat. The seat is subjected to strong flow impingement during oxygen gas discharge from the cylinder, due to the seat""s orientation above the valve nozzle. Further, due to the rotating seat mechanism, the seat often is subjected to strong frictional interference with the valve nozzle. Both of these features are undesirable to prudent persons aware of the fire hazards of handling oxygen cylinders. Conventional known valves are also xe2x80x9cdirty,xe2x80x9d generating large amounts of undesirable debris due valve). This debris often deposits in the nonmetallic seat itself and increases the frictional interactions during valve opening and closing.
These valves most often utilize a nylon main seat although both polyphenylene oxide (PPO) and polychlorotrifluoroethylene (PCTFE) are also utilized. Both Nylon and PPO exhibit poor to moderate compatibility based on present oxygen-compatibility rating test standards, and deliver a large amount of energy if ignited. PCTFE is considered an oxygen compatible material, but has a compressive modulus that is insufficient to withstand the torques that are often applied by the manual closing of valves. As a result, PCTFE seated plug-valves often exhibit significant extrusion and recently have been implicated in a large number of fires. The extruded seat increases the surface-area-to-volume ratio for oxygen gas impingement during discharge, and is believed to greatly increase vulnerability of the seat to hazardous flow friction ignition.
FIG. 1 depicts the generalities of known container-and- valve construction, shown in partial cross-section to reveal the function of interior elements. These types of containers are in common use by the millions around the world, to contain oxygen and other gasses under pressure for use. A known valve assembly, shown at 10, has a plug portion 11 threaded so to be securely screwed into the correspondingly threaded opening 12 at the xe2x80x9ctopxe2x80x9d end of a conventional pressurized gas cylinder 15 or tank. In this specification and in the claims, xe2x80x9ctopxe2x80x9d and xe2x80x9cbottomxe2x80x9d and xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d refer to a valve assembly and cylinder as oriented in FIG. 1, that is, with the axis of the cylindric container perpendicular to the ground, the valve sitting atop the cylinder and the planar bottom resting upon the ground. (This is the position in which conventional cylinder tanks are commonly stored and transported, although they are used in practically any position.) However, it must be clear that the present invention may be used with the container or tank in any position with respect to vertical or to the ground, including an inverted position in which the container is above the valve while in use.
In conventional gas container valves, sometimes called Sherwood valves, the handle 17 connects to a stem 21 which is retained inside the main body 20 by a cap or jam nut. The stem 21 engages a threaded plug 23 that has a screwed engagement with the body 20 of the valve 10. A valve seat 24, typically fashioned from nylon or a flexible plastic, is retained within the distal end of the plug 23. The main body 20 has a radial port 25 through which gas can enter and exit an upper chamber 27 defined in valve body 20. The body also has a lower or first chamber 28, located about the valve""s axis and via which gas may flow to and from the interior 13 of the container 15. The valve has an imaginary, central, longitudinal axis, generally describing the axis of symmetry of the body 20, and along which the handle 17 and stem 21 translate during operation. The body 20 defines an interior annular nozzle 30, a constriction dividing the lower chamber 28 from the upper, second chamber 27. The lower or first chamber 28 is in fluid connection with the second or upper chamber 27, as there is an orifice at the center of the nozzle 30 through which gas may flow. Rotation, e.g. manual rotation, of the handle 17 also rotates the stem 21 at the same rate, since the stem is connected to the handle. The plug 23 both rotates and translates in its threaded disposition within the body 20. Rotation of the handle and stem 21 thus cause the plug 23 to move axially, e.g. up and down, within the body 20. The seat 24 is contactable against the upper side of the nozzle 30 to close the nozzle orifice. Thus, the rotation of the handle 17 and stem 21 in the stem-engaging portion 19 shifts the plug 23 and seat 24 into and out of contact with the upper side of the nozzle to close and open the nozzle, and thus the valve 10, to the passage of gas. A helical spring 33 typically (but not necessarily) is employed to aid sealing of the stem packing seal. Standard clockwise rotation of the handle (as indicated by the directional arrow in FIG. 1) screws the plug 23 downward, and presses the seat 24 against the nozzle 30 to close the valve.
The foregoing commonly encountered valve design suffers from several functional drawbacks, especially when oxygen is the gas of interest. Most of the serious deleterious effects occur when a tank 15 containing oxygen under pressure is opened to discharge the oxygen for use. This discharging step is the most common circumstance of hazardous fire. Continued reference is made to FIG. 1. When the handle 17 is rotated counterclockwise to separate the seat 24 from the nozzle 30 to release oxygen under pressure from the interior 13 of the container 15, the high-velocity oxygen stream flows through the first conduit or chamber 28 and is further accelerated by passage through the orifice of the nozzle 30 en route to escape through the second port 25. Ordinarily, this high-velocity oxygen stream impacts directly upon the valve seat 24 immediately after passing through the nozzle 30. Fast-moving oxygen molecules impinging against a seat 24 commonly fashioned from nylon or plastic is a condition which fosters dangerous combustion of the seat. The combustion can then be spread downstream by the gas exiting the valve 10.
Also, it is noted that in known devices the separation of the seat 24 from the nozzle 30 occurs rapidly, i.e., just a partial rotation of the handle 17 and stem 21 may be adequate to disengage entirely the seat from the nozzle. Stated differently, the rotation of the stem 21 in the body 20 moves the seat rapidly upward, so that the axial distance of separation between the seat and the nozzle increases rapidly, resulting in a very quick change from a xe2x80x9cfully closedxe2x80x9d to xe2x80x9cmostly openxe2x80x9d flow condition. This rapid opening of the valve results in near adiabatic pressure changes which may heat valve components downstream, including the attached regulator. It also promotes deleterious mechanical friction and gas flow friction past the seat 24.
Further compromising the safety of conventional valves is the fact that the threaded portion of the plug 23 is xe2x80x9cwettedxe2x80x9d by the gas flow. The repeated frictional xe2x80x9cscrewedxe2x80x9d rotation of threaded metal parts past each other commonly generates very fine metal particles and shavings, and other minute debris. When such threaded parts are wetted by the gas flow through a valve 10, this particulate debris are freely released into the interior 13 of the container 15, or may dislodged by gas flow through the second chamber 27 or may be embedded in the seat 24. The high velocity impact of this debris against combustible elements in the system, particularly in oxygen systems, can kindle fires. Thus, a safer valve for use in oxygen systems should isolate from the gas flow any threaded components that move past each other in screwed engagement.
Finally, known valves do not readily accommodate the use of filters to prevent particle migration and impact against valve components. Debris (as, for example, from the screwed engagement of the rotatable stem 21 with the body 20, as described above, or from material that migrates into the interior 13 during cylinder filling) often falls into and accumulates within the interior 13 of the pressure cylinder 15. This accumulated debris is then available to be caught up by the gas stream from the container 15 during discharge, and whisked away to the valve 10 or downstream components where it can hazardously impinge against the seat 24 and/or other system components. A safer valve would prevent the movement of debris from within the cylinder 15 by filtering the gas entering the first chamber 28 from the interior 13. However, since particulate debris will be present and blown into the cylinder when it is being filled, safety concerns recommend that such a filter not be operative during the charging of the cylinder 15, lest hazardous debris accumulate on the xe2x80x9cwrongxe2x80x9d side of the filter where it can be blown back into the system when the cylinder is discharged.
A need remains, therefore, for a safer valve apparatus for use in pressurized oxygen systems. The invention was developed in response to this need. The inventive valve is designed to eliminate the common ignition mechanisms that have been observed in oxygen systems and to eliminate the weaknesses observed in known plug-type valves.
The invention is a valve apparatus. More particularly, a valve apparatus is provided that substantially reduces the risk of fire in high-pressure oxygen systems. The apparatus is particularly well-suited for use as a plug valve on ordinary cylinder containers, but may be beneficially used in any pressurized gas system, particularly oxygen or oxygen-enriched air systems such as those encountered in many industrial and medical facilities or underwater diving systems. The inventive valve, and its associated inventive check-filter and excess-flow prevention features, reduces the potential for hazardous combustion at valve points within oxygen delivery systems.
According to the invention, there is provided valve apparatus for controlling the flow of a gas between a high-pressure zone and a zone of lower pressure. The apparatus has a hollow body having a central axis, a threaded handle-engaging portion and a main portion; a first chamber and a second chamber, the chambers defined within the body and the first chamber in fluid communication with the high-pressure zone and the second chamber in fluid communication with the zone of lower pressure (which normally exists until the valve is fully opened); a nozzle within the body and separating the chambers, the nozzle defining an orifice for the passage of gas between the chambers; a rotatable threaded handle screwably engageable with the handle-engaging portion of the body; a stem rotatably connected with the handle whereby the handle may rotate with respect to the stem, and the stem having a distal portion; a seat on the distal portion of the stem and contactable with the nozzle to seal the orifice against the passage of gas; and at least one seal member disposed axially between the threaded handle-engaging portion and the second chamber. Rotation of the handle in the handle-engaging portion shifts the stem axially to move the seat into and out of contact with the nozzle, and wherein during its rotation, the handle rotates with respect to the stem, which is rotatably fixed in relation to the body.
The nozzle comprises a high-pressure (upstream) side adjacent the first chamber and a low-pressure (downstream) side adjacent the second chamber. In one embodiment, the stem is disposed in the second chamber and axial shifting of the stem moves the seat into and out of contact with the low-pressure side of the nozzle to close and open the orifice to the passage of gas there through. The seat may comprise an annular surface oblique in relation to the axis, wherein axial movement of the stem varies the distance between the oblique surface and the nozzle. This arrangement increases the loading contact area for the seat, reducing its load. It also reduces flow impingement by causing gas flow contact only on an angled plastic surface. Further, the nozzle may comprise an annular beveled surface defining a circumference of the orifice coaxial with oblique surface of the seat.
In a preferred embodiment, the stem is disposed in the second chamber and extends through the orifice, wherein the distal portion of the stem protrudes into the first chamber, and axial shifting of the stem moves the seat into and out of contact with the high-pressure side of the nozzle to close and open and close the orifice to the passage of gas there through.
Preferably, the stem comprises a xe2x80x9cthrottlingxe2x80x9d or choked flow portion disposed coaxially within the orifice, the throttling portion comprising an annular surface oblique in relation to the axis, wherein axial movement of the stem varies the distance between the oblique surface and the nozzle. The nozzle comprises an annular beveled surface defining a circumference of the orifice coaxial with the beveled surface. Preferably, the throttling portion and the nozzle each are made from a metal, wherein all choked flow of the gas during a charging flow and a discharging flow occurs between the throttling portion and the nozzle. Axial movement of the distal portion of the stem into the first chamber increases the distance between the oblique surface and the nozzle, wherein the rate of dilation of the distance between the oblique surface and the nozzle increases with continuing rotation of the handle. The proximate portion of the stem is in sliding contact with the body, and further comprising at least one seal member disposed radially between the proximate portion and the body, and axially between the threaded handle-engaging portion and the second chamber, wherein debris generated by the rotation of the handle in the handle-engaging portion is prevented by the stem and the seal member from entering the second chamber.
Also preferably, the handle is rotatable to move the stem between a closed position with the seat in contact with the nozzle and an open position with the seat out of contact with the nozzle; the stem is axially movable in relation to the handle, there is further provided means for biasing the stem axially away from the handle, so that when the stem is in the open position with the seat separated from the nozzle, if the gas pressure in the second chamber abruptly decreases, the resulting rapid change in the pressure gradient across the distal portion of the stem overcomes the compressive force of the means for biasing to automatically move the stem to the closed position to seal the orifice against the continued passage of gas there through.
A primary object of the present invention is to provide a valve which reduces the risk of hazardous combustion in gaseous oxygen delivery systems.
A primary advantage of the present invention is that the valve apparatus eliminates the possibility that debris generated by the action of threaded engagement between valve parts will find its way into the gas-wetted portion of the apparatus, by (a) isolating the wetted portions of the valve from the portions of the apparatus that abrade each other by screwed engagement, and (b) by providing a valve stem that does not rotate when the valve handle is rotated, yet rotation of the handle shifts the valve stem axially.
Another advantage of the invention is that fragile valve seat components are protected against the direct impact of high-velocity gases and any debris entrained therein.
Another advantage of the invention is that a check valve and filter mechanism is provided that permits foreign debris to enter a pressure tank, but which traps the debris behind a filter barrier to prevent the debris from entering a gas-delivery system.
Still another advantage of the invention is that it provides an excess-flow shut-off feature, so that the invention automatically stops the flow of gas there through in the event of a catastrophic leak, failure, or compromise in a downstream system.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.